L.A. Gurevich

Direct observation of the lattice of Abrikosov vortices in high-Tc superconductor YBa2Cu3Ox single crystals

Abstract The magnetic structure of the YBa2Cu3Ox single crystal has been investigated using the technique of decorating the sample with small ferromagnetic particles. The lattice of the Abrikosov vortices and the effects caused by pinning on the twin boundaries have been observed in both the electron and optical microscopes. The twin structure of the single crystals has been investigated using the polarized light in the optical microscope. The penetration depth for the magnetic field parallel to the c axis has been evaluated as ≲ 0.3 μm at 4.2 K for the YBa2Cu3Ox single crystal.

Observation of the flux line lattice in high Tc-superconductor Bi2.2Sr2CaCu2OX and Ti2Ba2CaCu2OX single crystals

Abstract The flux-line lattice (FLL) has been observed on the (001) face of high T c Bi 2.2 Sr 2 CaCu 2 O X and Ti 2 Ba 2 CaCu 2 O X single cristals using the technique of decorating the sample with small ferromagnetic particles. Strong pinning of the Abrikosov vortices by plane defects along (100) and (010) planes has been found out on Bi 2.2 Sr 2 CaCu 2 O X . The triangular FLL with a long-range order has been observed on the perfect Ti 2 Ba 2 CaCu 2 O X single crystal. The penetration depth for a magnetic field parallel to (001) axis has been evaluated as ≤0.2μm at 4.2K for both materials.

Direct observation of the vortex structure in high-Tc superconductors in tilted magnetic fields: II. Vortex pinning by twins in YBaCuO single crystals

The high resolution Bitter technique was used for observation of the vortex structure in twinned YBaCuO single crystal in the magnetic field tilted with respect both to the c-axis and to the twin planes. The dominating effect in vortex distribution was strong pinning by twin planes which was seen as an alignment of vortices along twins with approximately two times density higher density than in the bulk. This strong pinning remained unchange for a surprisingly broad interval of tilt angles 0<25°. For larger tilt angles, pinning did not disappear abrupity but the signs of a decrease of the effective pinning potential were observed-the difference of vortex density between twin boundaries and the bulk was gradually decreasing and finally disappeared at a critical angle as large as 42°. The observed behaviour is discussed in terms of the formation of zig-zag vortices partly pinned at twin planes.

Vortex structure in single-crystal high-Tc superconductors

The magnetic flux structure in type-II superconductors was predicted in 1957 by Abrikosov [5.1]. According to that theoretical work the magnetic field penetrates into a superconductor in the form of individual magnetic lines (vortices) each carrying one magnetic flux quantum Ф0 = hc/2e = 2.07.10−7 G.cm2. The idea of a vortex state proved to be extremely valuable in explaining electrodynamic properties of type-II superconductors. The most convincing evidence of the validity of this theory was the direct observation of the Abrikosov vortices using the high-resolution technique of decoration with dispersed ferromagnetic particles. This technique was developed in 1966 by Traumble and Essmann in Stuttgart [5.2]. Their works marked the beginning of magnetic structure investigations in conventional low-Tc type-II superconductors; the results have been summarized in reviews and monographs [5.3,5].